Protective circuit.



J. C. R. PALMER.

PROTECTIVE CfRCUIT.

APPLICATION FILED MAR. 9. 1915.

1 ,1 96,805. Patented Sept. 5,1916.

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JOEL C. R. PALMER, OF NEW ROCHELLE, NEW YORK, ASS IGNOR, BY 'MESNE ASSIGN- MENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION O]?- NEW YORK.

PROTECTIVE CIRCUIT.

Specification of Letters Patent.

' Patented Sept. 5, 1916.

Application filed March 9, 1915. Serial No. 13,272.

I Rochelle, in the county of Westchester and time interval is not great, the recurrent State of New York, have invented certain new and useful Improvements in Protective Circuits, of which the following is a full,

clear, concise, and exact description.

This invention relates to protective circuits, more particularly to a clrcuit arrangement in which a protecting resistance of the self regulating type, for example an iron ballast resistance, is included in circuit with a delicate current consuming device for the purpose of limiting the normal fiow of current therethrough. I

The object of this invention is to provide a secondary protection for such a current consuming device which shall operate' to protect said device from an excessive flow of current during such time as the normal protecting resistance may be ineffective so to function. a

It is a well known fact that an iron wire resistance preferably inclosed in a tube or other closed vessel and surrounded with an atmosphere of hydrogen is effective, within a given range depending upon its design, to

insure a substantially constant flow of current in the circuit of which it may form a part. Inasmuch, however, as the resistance of such an element when cold is considerably less than when heated, it follows that when the current flow through it is initiated it will not immediately present the necessary resistivity to prevent an excess flow of current through the device which it is intended to protect and a time interval will elapse before the resistance can build up to what may be called its regulative value. While this surges of current which it permits, where the circuit is closed and opened man times during a day, may be decidedly detrlmental to any sensitive apparatus included in the circuit. It has heretofore been proposed to bridge over this time interval by inserting a'slow acting device, such as a thermostat, in circuit with the ballast resistance and the deviceto be protected which shall maintain a, short circuit around said device for a sufiicieut length of time after the circuit is closed to allow the ballast resistanceto build up to its regulative value.

This invention insures a still further protection for a device of the type in question by providing an additional set of contacts on the thermostat, which when closed, reestablishes the short circuit on said device in case any of the apparatus in series therewith becomes short circuited or if for any other reason an undue current flow occurs.

- In the accompanying drawing the invention is illustrated as applied to the filament heating circuit of an audion repeater.

Referring to the drawings 3, a and 5 are respectively the filament, grid and plate elements of an audion, 6 a retardation coil, 7 a battery, 8 a circuit closing switch, 9 a ballast resistance and 10 is a thermostat composed of a bimetallic strip 11 of the well known type and a heating coil 12, and pro-,

vided with contact points 13 and 14.

In the cold condition of the thermostat 10, the strip 11 makes contact with the point 13. When therefore the switch 8 is closed current Will flow from battery 7 through coil 6, by way of the contact between point 13 and strip 11 through heating winding 12, ballast resistance 9 and switch 8 back to battery. As the bimetallic strip 11 becomes heated by the flow of current through winding 12, it will warp away from point 13 and open the short circuit around filament 3 which originally existed. By the time this takes place the ,ballast 9 will have reached its regulative value of resistance and will thenceforth function to maintain a steady flow of current through the filament. If, however, the ballast 9 or, the retardation coil 6 becomes short circuited the heating effect of the additional current flow occasioned thereb will cause the strip to warp still farther 1nto the position indicated by the dotted outline, in which position it makes contact with point 14, again establishing the short circuit around filament 3 and protecting it from permanent injury.

W at'is claimed 1s: A protective circuit comprising a current consuming device to be protected, a ballast resistance adapted when heated, to regulate the normal fiow of current through said device, a low resistance path in parallel with I said device, a slow acting current actuated means operating upon the closure of said circuit to open said low resistance path, after 1915.

said ballast resistance shall have become 5 heated and operating to reestablish said low resistance path when an excessive current flows in said circuit.

meeeee In Witness v vhereo-f, I hereuntd subscribe Witnesses: 4 4 E. EDLER,

K. L STAHL. 

